Old O/U by SAUER and Sohn, SUHL.

Need some expert eyes to pass over my new gun.
Came to me yesterday, she's got 28" barrels, 12g, Circa 1920 so I was led to believe, but so light for a game gun, she like a feather, say 6.5 I reckon.

I just wondered if anyone is able to tell me date of manufacture? Present worth/value and if I will be able to source any original accessories/labels for this gun, what sort of case it may have had etc. Barrels show its Nitro proofed, would this have been done some time after manufacture?